The overall objective of this program is an improved understanding of the structure and function of eukaryotic chromosomes. Our investigations center on the fruit fly which has the advantages of extensive genetics and giant polytene chromosomes. During the coming year efforts will be concentrated on a joint cytological and biochemical search for the induction of new cell functions in response to radiation damage. Recent studies performed in mammals offer strong support for the existence of such a response. Our preliminary studies demonstrate a similar response in Drosophila. The purpose of this study is to employ the powerful genetic advantages of Drosophila to bridge the gap between studies of repair induction in mammals and bacteria. Such systems have been strongly implicated in mutagenesis and therefore possibly carcinogenesis.